This invention deals with pivot joint assemblies having provisions for indicating the wear of their component parts. More specifically, the invention pertains to a ball and socket joint, suitable for use in automotive wheel suspensions in particular, that makes a clearly discernible indication when the joint wears in use beyond a tolerable limit.
Wear indicating pivot joint assemblies are per se not new in the art. Examples of such known joints are described and claimed in U.S. Pat. No. 3,813,178 and British Pat. No. 1,336 087. Both suggest an externally visible protrusion that retracts into the joint housing with the development of wear. The full retraction of the protrusion into the housing indicates that the joint is worn enough to warrant replacement. These prior art devices are unsatisfactory, however, as the protrusion retracts at a rate equal to or less than the amount of the wear of the joint part. Thus the stroke of the protrusion is only from 1.0 to 1.5 millimeters. Moreover, since the protrusion initially projects to varying degrees because of unavoidable dimensional errors in manufacture, the visual recognition of the exact moment the conventional joints are in need of replacement has been difficult.
The noted U.S. Pat. No. 3,813,178 also teaches the use of a metal or plastic cap that is pressed or snapped on the protrusion. Being bottomed against the joint housing. the cap is released from the protrusion upon retraction thereof into the housing. The thus bared protrusion indicates, then, that the joint must be replaced.
The use of the cap is in itself favorable since it leads to a clearer indication of whether the joint is worn or not. However. the pressfitted cap has been easy to come off the protrusion in the use of the joint in a vehicular suspension, as by being hit by a stone that has been sent up by the vehicle. Additionally, after the detachment of the cap, either accidentally or otherwise, dust has been easy to accumulate on the bared protrusion, making it impossible to discern whether it is capped or uncapped.